Even Adele, in her current No. 1 hit, “Rolling in the Deep,” warns an ex-lover, “Go ahead and sell me out, and I’ll lay your ship bare.”

Evidence of sexual economics — a mashup of Adam Smith and Dr. Ruth that seeks to explain how the “sexual market” works — is everywhere, said University of Texas sociology professor Mark Regnerus.

“One of the biggest unacknowledged facts about sex is the underlying economy to it all,” he said. “When you look into it, it’s really amazing how it works. And it’s fairly elementary as well: We put a price tag on sex. You might not think we ought to do that, but we do. Sex, at one level, is an exchange. … Each person gives the other person something of themselves. But it is typically a different something.”

Mr. Regnerus and co-author Jeremy Uecker use sexual economics theory in their new data-driven book, “Premarital Sex in America: How Young Americans Meet, Mate and Think About Marrying.”

Their conclusion is that, for young single Americans, modern rules of romantic engagement “clearly favor men” and penalize women who want to marry — especially those who want to save sex for marriage.

So what was the old “exchange rate” for sex, and how has it changed? Researchers have long recognized that male-female mating systems revolved around exchanges. Even in ancient times, men and women bonded because one could cook, sew, make a home and have babies, and the other could hunt prey and protect the woman and child, Evergreen State College historian Stephanie Coontz recounted in her 2005 book, “Marriage, a History.”

Exchange rates sometimes involved real money or property, in the form of dowries or bride prices, she noted.

Sociologist Linda Waite and syndicated columnist Maggie Gallagher looked at another element of sexual economics in their 2000 book, “The Case for Marriage: Why Married People Are Happier, Healthier and Better Off Financially.”

The reasons for this prosperity include a real-but-unwritten “wage premium” that husbands frequently earn and the prodigious ability of wives to save and hunt for bargains, they wrote.

The birth-control pill rewrote rules about sex and mating, Mr. Regnerus said during a recent forum at the Heritage Foundation think tank. Before the birth-control pill, the sexual market was strongly linked to the “marriage market.”

A man who sought sex with a particular woman typically had to give her something of very high value in exchange — either marriage or at least a marriage proposal, he said. This is because female sexuality has high value to men, he said, citing the seminal paper on sexual economics by Florida State University sociologist Roy Baumeister and consumer psychologist Kathleen Vohs.

However, the birth-control pill disconnected the sexual and marriage markets, and now both men and women typically enter the sexual market first.

The sexual market generally has more men than women in it, and rules of supply and demand operate, with the rarer sex wielding more power, Mr. Regnerus said.

Say a young man wants to get to know his girlfriend of two months “more,” he said. If she says no, “then this tells the man, ‘The price is higher than you think.’ And he will have to figure out how high the price is: Does she need more time, more commitment?”

Not all sexual markets are overpopulated by men, Mr. Regnerus said. College campuses and urban areas are often dominated by women, which means that men can and will decide how much — or how little — they will exchange for sex.

Men’s rules of engagement play to their interests of having sex often, with many partners, in a more sexually permissive environment, without romance or commitment, he said.

To be sure, many young women “don’t mind this new sexual economy. Plenty of them like to spend some time in the sex market before moving on to the marriage market,” Mr. Regnerus said.

The problem, he said, is that women can “underestimate the long-term risk of sex-market behavior.”

Although plenty of women dabble in sexual-market relationships and then settle down successfully with life partners, he said, many women are “not witnessing marriage happening on the timetables they prefer and expected.”

This is because, as economist Timothy Reickert has found, power shifts away from women as they move toward their 30s, Mr. Regnerus said. In other words, women have power when they are the minority in the sex market, but they lose power when they drift into the marriage market, where women outnumber men.

“One reason I am doing this research is to help people who want to get married to make it happen,” Mr. Regnerus said.

The new sexual economy is especially disadvantageous to any woman who wants to remain a virgin until her wedding day, he said. These women essentially never enter the sex market, but instead “hold out for the highest price for sex, which is marriage.”

Today, that is a high-risk strategy, Mr. Regnerus explained, using a housing-market analogy: “You can’t just decide that your house is worth $500,000 if everyone else is getting $200,000. … You can try for that price, but it’s unlikely you will get it.”

What are women to do if they don’t like the current sexual economics?

A fundamental principle of sexual economics is that “sexual activity by females has exchange value, whereas male sexuality does not,” Mr. Baumeister and Ms. Vohs wrote in their 2004 paper.

Thus, women have the power to influence sexual norms were they to use it, Mr. Regnerus said.

“When women collude to restrict men’s sexual access to women, all women tend to benefit,” he said, noting that “if women were more in charge of how their romantic relationships transpired … we would be seeing greater male investment in relationships, more impressive wooing efforts, fewer hookups, fewer premarital sexual partners … shorter cohabitations, more marrying … and more marrying at a slightly earlier age. In other words, the price of sex would be higher. It would cost men more to access it.”

However, he said, “none of these things are occurring today. Not one. The price of sex is pretty low.”